smgr.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * smgr.h
 *    storage manager switch public interface declarations.
 *
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/smgr.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SMGR_H
#define SMGR_H

#include "lib/ilist.h"
#include "storage/block.h"
#include "storage/relfilenode.h"

/*
 * smgr.c maintains a table of SMgrRelation objects, which are essentially
 * cached file handles.  An SMgrRelation is created (if not already present)
 * by smgropen(), and destroyed by smgrclose().  Note that neither of these
 * operations imply I/O, they just create or destroy a hashtable entry.
 * (But smgrclose() may release associated resources, such as OS-level file
 * descriptors.)
 *
 * An SMgrRelation may have an "owner", which is just a pointer to it from
 * somewhere else; smgr.c will clear this pointer if the SMgrRelation is
 * closed.  We use this to avoid dangling pointers from relcache to smgr
 * without having to make the smgr explicitly aware of relcache.  There
 * can't be more than one "owner" pointer per SMgrRelation, but that's
 * all we need.
 *
 * SMgrRelations that do not have an "owner" are considered to be transient,
 * and are deleted at end of transaction.
 */
typedef struct SMgrRelationData
{
    /* rnode is the hashtable lookup key, so it must be first! */
    RelFileNodeBackend smgr_rnode;  /* relation physical identifier */

    /* pointer to owning pointer, or NULL if none */
    struct SMgrRelationData **smgr_owner;

    /*
     * These next three fields are not actually used or manipulated by smgr,
     * except that they are reset to InvalidBlockNumber upon a cache flush
     * event (in particular, upon truncation of the relation).  Higher levels
     * store cached state here so that it will be reset when truncation
     * happens.  In all three cases, InvalidBlockNumber means "unknown".
     */
    BlockNumber smgr_targblock; /* current insertion target block */
    BlockNumber smgr_fsm_nblocks;   /* last known size of fsm fork */
    BlockNumber smgr_vm_nblocks;    /* last known size of vm fork */

    /* additional public fields may someday exist here */

    /*
     * Fields below here are intended to be private to smgr.c and its
     * submodules.  Do not touch them from elsewhere.
     */
    int         smgr_which;     /* storage manager selector */

    /*
     * for md.c; per-fork arrays of the number of open segments
     * (md_num_open_segs) and the segments themselves (md_seg_fds).
     */
    int         md_num_open_segs[MAX_FORKNUM + 1];
    struct _MdfdVec *md_seg_fds[MAX_FORKNUM + 1];

    /* if unowned, list link in list of all unowned SMgrRelations */
    dlist_node  node;
} SMgrRelationData;

typedef SMgrRelationData *SMgrRelation;

#define SmgrIsTemp(smgr) \
    RelFileNodeBackendIsTemp((smgr)->smgr_rnode)

extern void smgrinit(void);
extern SMgrRelation smgropen(RelFileNode rnode, BackendId backend);
extern bool smgrexists(SMgrRelation reln, ForkNumber forknum);
extern void smgrsetowner(SMgrRelation *owner, SMgrRelation reln);
extern void smgrclearowner(SMgrRelation *owner, SMgrRelation reln);
extern void smgrclose(SMgrRelation reln);
extern void smgrcloseall(void);
extern void smgrclosenode(RelFileNodeBackend rnode);
extern void smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
extern void smgrdounlink(SMgrRelation reln, bool isRedo);
extern void smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo);
extern void smgrextend(SMgrRelation reln, ForkNumber forknum,
                       BlockNumber blocknum, char *buffer, bool skipFsync);
extern void smgrprefetch(SMgrRelation reln, ForkNumber forknum,
                         BlockNumber blocknum);
extern void smgrread(SMgrRelation reln, ForkNumber forknum,
                     BlockNumber blocknum, char *buffer);
extern void smgrwrite(SMgrRelation reln, ForkNumber forknum,
                      BlockNumber blocknum, char *buffer, bool skipFsync);
extern void smgrwriteback(SMgrRelation reln, ForkNumber forknum,
                          BlockNumber blocknum, BlockNumber nblocks);
extern BlockNumber smgrnblocks(SMgrRelation reln, ForkNumber forknum);
extern void smgrtruncate(SMgrRelation reln, ForkNumber forknum,
                         BlockNumber nblocks);
extern void smgrimmedsync(SMgrRelation reln, ForkNumber forknum);
extern void AtEOXact_SMgr(void);

#endif                          /* SMGR_H */